.left-side {
    position: absolute;
    left: 0;
    top: 0;
    width: 20%;
    height: 100%;
    background-color: lightgray;
}

.container {
    position: absolute;
    left: 20%;
    top: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    width: 80%;
    height: 100%;
}

textarea {
    width: 50%;
    height: 50%;
}